1. Field of the Invention
The present invention relates to a control device for cutting the supply of fuel to an engine (internal combustion engine) for a vehicle during the deceleration of the vehicle and to a device for controlling the blow-out rate of a compressor in an air-conditioning device mounted on the vehicle equipped with the above control device.
2. Description of the Related Art
In the vehicles, so far, it is an accepted practice to execute the so-called fuel-cut control operation for cutting the supply of fuel to the engine of the vehicle in order to improve the fuel efficiency during the deceleration operation in which the accelerator operation amount (amount the accelerator pedal is depressed) is zero. In order to prevent the vehicle engine from coming into a halt (to prevent the engine stalling), in this case, a predetermined lower-limit rotational speed Neo (e.g., 800 rpm) at which the vehicle engine still continues to run even if the supply of fuel is cut is set as a rotational speed for resetting the cut of fuel supply. The supply of fuel is resumed when the engine rotational speed becomes smaller than the lower-limit rotational speed Neo.
In a vehicle mounting the air-conditioning device, the load exerted on the engine increases by the amount the compressor load torque exerts on the engine when the air-conditioning device is in operation as compared to when it is not in operation. Accordingly, the lower-limit rotational speed Neo for resuming the supply of fuel is set to be higher by a predetermined amount xcex1 (e.g., 200 rpm). That is, with the air-conditioning device being in operation, the supply of fuel is resumed when the engine rotational speed becomes smaller than Neo+xcex1 (e.g., 1000 rpm).
The above-mentioned value+xcex1 has been determined by taking a maximum load torque of the compressor into consideration to reliably prevent the engine stalling. However, an inconvenience that is described below occurs.
That is, in small cooling load conditions, such as in spring and in fall, the compressor needs to blow out the coolant at a low rate (low flow rate per unit time). When the compressor is of the variable capacity type, therefore, the compressor is operated in a low capacity state. The load torque of the compressor varies in proportion to the blow-out capacity. When the compressor is operated in a low capacity state, therefore, the supply of fuel is resumed at a high rotational speed which is Neo+xcex1 though the cut of fuel supply can be maintained even at a rotational speed lower than Neo+xcex1, causing the engine to wastefully consume fuel.
Japanese Unexamined Patent Publication (Kokai) No. 8-312423 discloses an art in which a second setpoint rotational speed for resuming the fuel supply in the case that the air-conditioning device is in operation is set to be higher than a first setpoint rotational speed for resuming the fuel supply in the case that the air-conditioning device is not in operation, and the supply of fuel amount to the engine is controlled to be lean when the air-conditioning device is operated with the engine rotational speed lying between the first setpoint rotational speed and the second setpoint rotational speed.
Even according to this prior art, however, the setpoint rotational speed at the time of resuming the fuel supply is increased or decreased depending upon whether the air-conditioning device is in operation or not in operation. Therefore, fuel is wastefully consumed in low cooling load conditions.
In view of the above-mentioned situation, it is an object of the present invention to provide a device for controlling an engine for a vehicle capable of suitably controlling a period in which the fuel supply is cut by estimating a load torque of an air-conditioning compressor under a condition for resuming the fuel supply.
It is another object of the present invention to provide an air-conditioning, device for a vehicle capable of suitably controlling the blow-out rate of the air-conditioning compressor by estimating a load torque of the air-conditioning compressor under the condition for resuming the fuel supply.
The present invention was contrived in order to accomplish the above objects. An air-conditioning device for a vehicle according to an embodiment of the invention comprises blow-out rate varying means (19) for varying the blow-out rate of a compressor (1) driven by a vehicle engine (4), and load torque estimating means (S400) for estimating a physical quantity related to the load torque of the compressor (1) under a condition of resuming the fuel supply after the fuel supply has been cut, wherein the blow-out rate of the compressor (1) is changed by controlling the blow-out rate varying means (19) depending upon an estimated value of physical quantity output from the load torque estimating means (S400).
This makes it possible, at the time when the fuel supply is cut, to set a suitable blow-out rate of the compressor corresponding to an estimated value of the compressor load torque under the condition of resuming the fuel supply.
Concretely speaking, in this case, the blow-out rate of the compressor (1) can be changed {circumflex over (1)} by using a variable capacity-type compressor, or {circumflex over (2)} by using a fixed capacity-type compressor (1) having a constant blow-out rate, by interposing a speed-change apparatus, between the compressor (1) and the vehicle engine (4), of which the speed-change ratio can be controlled by a control signal from an external unit, and by changing the rotational speed of the compressor (1) by changing the speed-change ratio of the speed-change apparatus.
It is further allowable to set a reference value related to load torque of the compressor (1) under the condition of resuming the fuel supply and to vary the blow-out rate of the compressor (1) so that the estimated value of physical quantity approaches the reference value.
According to this method, if the reference value of the compressor load torque is set to be a limit value at which the operation characteristics of the vehicle engine (4) are still maintained in a favorable zone, then the blow-out rate of the compressor is changed so that the compressor load torque under the condition of resuming the fuel supply approaches the limit value at which the engine operating characteristics are still maintained in the favorable zone.
Therefore, when there is a margin in the engine output while maintaining the engine operation characteristics in the favorable zone, the blow-out rate of the compressor is increased to increase the cooling ability in the refrigeration cycle in order to increase the effect of recovering energy during the deceleration.
The above reference value may be the load torque of the compressor at the time of resuming the fuel supply under the condition of a maximum air-conditioning load.
In the air-conditioning device for vehicles according to another embodiment of the invention, a reference value related to load torque of the compressor (1) is set under the condition of resuming the fuel supply, and the blow-out rate of the compressor (1) during the control operation for cutting the fuel supply is increased to be larger than the blow-out rate at the time when the control operation for cutting the fuel supply is started in the case that the estimated value of physical quantity output from load torque estimating means (S400) is smaller than the reference value, and the blow-out rate of the compressor (1) during the control operation for cutting the fuel supply is decreased to be smaller than the blow-out rate at the time when the control operation for cutting the fuel supply is started in the case that the estimated value of physical quantity is larger than the reference value.
This makes it possible to maintain the engine operation characteristics in the favorable zone as well as to increase the effect of recovering energy during the deceleration by increasing the blow-out rate of the compressor.
In the case that the estimated value of physical quantity is smaller than the reference value, the blow-out rate of the compressor (1) during the control operation for cutting the fuel supply may be forcibly brought to be a maximum blow-out rate.
The load torque estimating means (S400) is capable of estimating the physical quantity based upon the physical quantity related to the load torque of the compressor (1) and the rotational speed of the compressor (1) at the time when the control operation for cutting the fuel supply is started, and upon the rotational speed of the compressor (1) under the condition of resuming the fuel supply.
Described below is the method for estimating the load torque. Deceleration of the vehicle continues for only a short period of time and, hence, the time for cutting the fuel supply inevitably becomes short. During this period, therefore, it is considered that the air-conditioning thermal load is maintained constant. While the control operation for cutting the fuel supply is executed, therefore, the blow-out rate of the compressor is maintained constant from the standpoint of the air-conditioning thermal load. By utilizing this relationship, it is possible to accurately estimate the load torque of the compressor under a condition of resuming the fuel supply from the compressor dynamic condition (torque and rotational speed) at the time when the control operation for cutting the fuel supply is started and from the rotational speed of the compressor under the condition for resuming the fuel supply.
Here, the timing for starting the control operation for cutting the fuel supply is not strictly limited to only a timing for starting the cut of the fuel supply, but may be just before or just after when the fuel supply is cut.
Here, further, the condition for resuming the fuel supply may concretely be a timing of when the rotational speed of the vehicle engine (4) has dropped down to a predetermined rotational speed after the fuel supply has been cut.
A further embodiment of the present invention is concerned with a device for controlling an engine for a vehicle which cuts the fuel supply to a vehicle engine (4) under a predetermined condition during the deceleration of the vehicle, and which mounts an air-conditioning device having a compressor (1) that is driven by the vehicle engine (4), compresses the coolant in a refrigerating cycle and blows the coolant out, the device for controlling the engine for a vehicle comprising:
load torque estimating means (S400) for estimating a physical quantity related to the load torque of the compressor (1) under a condition for resuming the fuel supply; and
fuel supply resumption control means (S700a) for changing the timing for resuming the fuel supply depending upon the estimated value-of physical quantity output from the load torque estimating means (S400).
This makes it possible to suitably control the period in which the fuel supply is cut by estimating the load torque of the air-conditioning compressor under the condition for resuming the fuel supply and by suitably determining the timing for resuming the fuel supply (the timing for resetting the cut of fuel supply).
The reference value related to load torque of the compressor (1) is set under the condition for resuming the fuel supply, and in the case that the estimated value of physical quantity is smaller than the reference value, the timing for resuming the fuel supply may be delayed so that the operation characteristics of the vehicle engine (4) approach a border line between the defective zone (D) and the favorable zone (E).
When the estimated value related to the load torque of the compressor is smaller than the reference value, i.e., when there is still a margin in the engine output, therefore, the timing for resuming the fuel supply is delayed to lengthen the period in which the fuel supply remains cut, in order,to decrease the consumption of fuel without deteriorating the engine operation characteristics.
The above reference value may be the load torque of the compressor at the time of resuming the fuel supply under the condition of a maximum air-conditioning load. in a device for controlling an engine for a vehicle according to a still further embodiment of the present invention, a reference value related to load torque of the compressor (1) is set under the condition of resuming the fuel supply, the timing for resuming the fuel supply is delayed behind the timing that is set based on the reference value when the estimated value of physical quantity is smaller than the reference value, and the timing for resuming the fuel supply is advanced ahead of the timing that is set based on the reference value when the estimated value of physical quantity is larger than the reference value.
Namely, when the estimated value related to load torque of the compressor is smaller than the reference value, the timing for resuming the fuel supply is delayed to lengthen the period for cutting the fuel supply, in order to decrease the consumption of fuel. When the estimated value related to load torque of the compressor is larger than the reference value, on the other hand, the timing for resuming the fuel supply is advanced to avoid deterioration in the engine operating characteristics in advance.
The load torque estimating means (S400) can estimate the physical quantity based upon the physical quantity related to the load torque of the compressor (1) and the rotational speed of the compressor (1) at the time when the control operation for cutting the fuel supply is started and upon the rotational speed of the compressor (1) under the condition of resetting the cut of fuel supply.
Then, as described earlier, it is possible to accurately estimate the load torque of the compressor under the condition of resuming the fuel supply from the dynamic conditions of the compressor (torque and rotational speed) at the time when the control operation for cutting the fuel supply is started and from the rotational speed of the compressor under the condition for resuming the fuel supply.
Numerals in parentheses in the above-mentioned means are to represent correspondence to concrete means described in the embodiments appearing later.